Siemens introduces Medium Voltage Direct Current System in North America
- Efficient power transmission ranging from 30 to 150 megawatts
- Functions as direct-current transmission line (DC) to control, optimize, and regulate load flows in medium-voltage alternating current grids (AC)
- Based on Siemens high-voltage direct-current transmission (HVDC) technology
Siemens announced this week at the IEEE T&D Conference in Denver that it is introducing a new direct-current transmission system, Medium Voltage Direct Current Power Link Universal System (MVDC PLUS), in the North American market. MVDC PLUS can efficiently bridge distances of up to 200 kilometers, or about 120 miles, and transmit electricity in medium-voltage AC grids from 30 to 150 kilovolts (kV) to help grid operators keep networks stable and handle a growing share of power generated from distributed and renewable energy sources. Siemens offers the medium-voltage DC transmission system in three compact capacities – approximately 50, 100, and 150 megawatts (MW) at DC transmission voltages of 20 to 50 kV.
MVDC PLUS can help connect small and remote communities to the grid, and also connect and stabilize low-power distribution grids regardless of their voltage and frequency. The medium-voltage DC transmission system is cost effective, and includes a flexible financing model, making it ideal for gird operators to quickly deploy to help meet the growth of renewable and distributed energy sources across North America.
“The expansion of wind power and solar energy systems has huge consequences for the transmission and distribution of electricity. As power generation becomes more complicated and decentralized, new risks arise with power quality and grid stability,” said Mirko Düsel, CEO Transmission Solutions at Siemens Energy Management. “MVDC allows operators to manage short-circuit currents and optimize networks through a hybrid approach, using a mix of AC and DC. This in turn reduces investment costs as MVDC is simply more economical than MVAC because it offers a higher capacity at lower voltage.”
This system can help regulate power exchanges between regional, medium-voltage networks and microgrids with greater independence from high-voltage networks. MVDC PLUS supports a wide range of customers because it can transmit power over cables and overhead lines while leveraging existing routes to increase power capacity without the need to move up to high-voltage levels.
Additionally, the transmission system allows operators to set up a power link between islands, or offshore platforms, and the mainland which could replace diesel generators used for backup power. This replacement would help to avoid maintenance delays and reduce emissions from generators that typically run on fossil fuels. MVDC PLUS can also be used as a backup power solution for manufacturing industries that rely on medium-voltage transmission to increase equipment availability and reduce machine downtime. This solution was also designed to supply backup power to data centers with classification in a quality stage (“tier").
MVDC technology is based on the HVDC PLUS technology used in the Siemens HVDC transmission system, but is reduced to its basic functions. Like HVDC PLUS, the medium-voltage transmission system operates with voltage-source converters (VSC) in a modular multilevel converter design (MMC) that converts alternating current into direct current and vice versa which can flow in both directions. Using insulated-gate bipolar transistors (IGBT), the commutation processes in the converter can run independently of the network’s voltage. Both converter stations can be operated as a static synchronous compensator (statcom). The high-speed control and protection intervention capabilities of the converters ensure the stability of the transmission system, which reduces network malfunctions in the three-phase grid. This reduction significantly improves reliability for energy suppliers and customers.